The present invention refers to a device, implantable in a living organisms, for the utilisation of at least part of the hydraulic energy developed by the heart (the primary unit), which is acquired by the natural work of the heart i.e. by the contraction of the heart (the systolic phase) where the blood is put under pressure, followed by the relaxation phase (the diastole), where the ventricles of the heart are filled with blood. The device comprises at least one secondary unit connected to the cardiovascular system.
The heart is well known to work as two deplacement pumps which are functionally separated apart, and which work syncronously, in the way that the right pump transports blood to the the pulmonary circulation, whereafter the oxygenated blood returns to the left pump. Thereafter, the left side ejects the oxygenated blood to the peripheral circulation of the body i.e to the vascular system of the entire organism. Finally, the blood returns to the inlet of the right pump.
The force of the pump is generated by the contraction of the cells of the myocardium, which surround the atria and the ventricles of the heart. The direction of the circulation is controlled by unidirectionally acting valves. The energy delivered by the heart to the surrounding, mainly to the blood consists primarily of pressure-volume work against the blood, kinetic work and heat.
It is previously known to assist the circulation, when the heart is fainting, by external force. Such assist is typically powered by pressurized air or electricity as energy source located outside the body. It has even been suggested to utilize energy converted from muscle, other than the heart, for example muscle of the legs, or from the back, as energy for the circulating blood via some sort of converting mechanism.
To add energy, from outside the body, to implanted assist devices has previously been used and is principally not difficult. But it may cause discomfort and be complicated for the patient due to tubings and cables penetrating the skin. Such connections limit the patient""s degree of freedom to special rooms or to trolleys equipped with batteries and computers. If therefore, one could use energy existing within the body, the patient would experience a new degree of freedom. The circulation of living creatures, including man, is normally kept in balance between the cardiac output and the resistance of the peripheral arteries, in the way that blood pressure is kept within narrow limits. This is necessary since several organs cannot work and/or survive if the blood pressure drops below, or increases above extreme levels. The kidneys and the brain are organs known to be sensitive to variations in blood pressure. Thus, if the heart in a human being faints, and cannot pump out the blood with enough force to keep the arterial mean blood pressure slightly above 50 mm Hg, the person will loose consciousness. If the kidneys are exposed for a similarly low arterial pressure, at least if exposed for a considerable long time, the urine production will cease. When the heart is fainting, and for some reason or another cannot generate a sufficiently high blood pressure, the person will die. This is through for left side fainting, but also for right side fainting if the right pump cannot overcome the resistance of the lungs.
The fact that the heart sometimes cannot pump out the blood to the circulation with a sufficiently high pressure does not necessarily mean that the heart cannot deliver enough energy to the circulation, if mechanical, and other conditions, were correct. In contrary, several examples can be given, where the heart is extremely powerful and has hypertrophied to a size 2-3 times the normal, over years, but still the pressure is low. One typical example for such a situation, is a heart with one ore more valves leaking, or a dilated heart, which cannot deliver a sufficiently high pressure to the circulation. The energy consumption of such a heart is much higher than the normal delivery to the circulation at rest (1 watt). The efficiency, i.e. the PVxe2x88x92energy+the kinetic energy/ the total energy for a normal heart is around 15%, while for a diseased heart, especially if dilated the efficiency is considerably lower than that.
A normal heart has a relatively low efficiency as a pump, compared to industrial pumps. Energy losses do arise (among other things) since the ventricles, at each contraction, as first step, have to generate a contraction of the ventricular wall, which allows the ventricular pressure to reach the aortic pressure (or the pressure of the pulmonary artery for the right pump); the ventricle wall is pre-tightened. This contraction leads to energy losses, which are proportional to the diameter of the ventricles in square, and therefore, these losses are great when the ventricles are dilated. In the second phase of the contraction, the ventricles have to increase the tension of the ventricular wall further, resulting in a ventricular pressure higher than the aortic pressure whereby the ejection of the blood takes place. During the ejection, the volume of the ventricles decreases, and therefore, the wall thickness of the ventricles increases. This remodeling of the muscle mass also leads to energy losses which in some diseases (for example at extremely hypertrophic hearts) may be considerable.
The way more than normal energy can be extracted from a fainting heart, is realized by comparing the pressure volume relation demonstrated in FIG. 1, which is en example given for a healthy heart (with an ejection fraction of 80%), with the relation given in FIG. 2, for a diseased heart (with an ejection fraction of 40%). Both figures are presented as PV-diagrams. The pressure-volume curve appears as a modified square anti-clockwise and the area within the loop represents the work of the heart (EW=External Work) on the blood. The area PE represents energy within the heart converted to heat at each contraction of the heart, which therefore is to be considered as wasted energy.
It is noted that the area of the surface PE (in FIGS. 1, 2 and 3) is not directly correlated to the one of the EW surface. The PE-area is proportional against the wasted energy but must be multiplied by a factor over 10 in a weak heart.
FIG. 2 is an example of how a diseased heart works. In order to achieve same minute volume and frequency as a healthy heart, blood is retained within the ventricle after each contraction and even the mean pressure is below normal level. The efficiency of the heart is decreased.
The fact that retained blood within the ventricle after each contraction does lead to energy loss should not be considered as if the retained blood should possess potential energy released in diastole. This is not the case since the blood is not compressible. In contrast, energy is lost since the ventricle must be pre-tightened before it can create a pressure high enough to start the ejection of the blood. This pre-tightening is well known energy consuming and is proportional to the volume of the ventricle.
Besides this factor, there are several other important factors that decide the oxygen consumption of the heart and thereby the energy consumption, the magnitude of the lost energy and the efficiency of the heart. These are described in the book xe2x80x9cThe Heart Arteries and Veinsxe2x80x9d 8 Edition. McGraw-Hill Inc., being for example the mass of the heart, the level of the pre-tightening, the frequency of the heart and the hormones influencing the heart. In contrast, as a paradox, the external work of the heart is not the main factor to decide the oxygen consumption since maximally 15% of the energy of the heart is converted to external work (for a healthy heart). When a heart weakens, often first step is a dilatation of the ventricle, later through an increase of its mass whereby the losses increase dramatically.
The idea to take out more blood at the contraction of the ventricles (systolic phase) is old and used every day. Pharmacologically it is easy to dilate the capacitance vessels of the arterial system (i.e. an afterload reduction) and thereby increase the stroke volume and the minute volume. But the price is low blood pressure and the limits within one operates are narrow. Likewise, one can influence the heart mechanically to eject more blood in each cycle. This may for example be achieved by diastolic counterpulsating, and one example of such pumps is the aortic balloon pump.
A diastolic counterpulsator works in its simplest form in the way that when the heart in systolic phase ejects its contained blood, the counterpulsator accumulates part of this volume outside the cardiovascular system for example in a pump cylinder connected to the artery in a groin. Thereby, the systolic resistance is reduced and the systolic blood pressure is kept low which ameliorates the ejection of the blood from the heart.
In diastolic phase, when the valve between the heart and the arterial system is closed, an external force, i.e. a motor, is used to press back the blood from the counterpulsator to the arterial system. The diastolic pressure is increased, as is the mean pressure. It is noted that this way of pumping results in a mirrored arterial blood pressure curve. This is true for external counterpulsators as described above, but also for internally located counterpulsators like the aortic balloon pump, which is the most commonly used assist pump in modern cardiac surgery. The mechanism is simple and intelligentxe2x80x94bit it needs externally added energy.
The counterpulsator is a device well described in the medical literature i.e. xe2x80x9cCardiopulmonary Bypassxe2x80x9d by Kenneth M. Taylor, 1986. Chapman and Hall Ltd., 9 chapter.
By U.S. Pat. No. 4,938,766xe2x80x94R. Jarvikxe2x80x94is known an implantable prosthesisxe2x80x94a devicexe2x80x94for amelioration of the perfusion of the natural cardiovascular system without adding energy from outside the body. However, the device cannot store the energy for more than part of a cardiac cycle. Nor can it render the arterial pressure curve in mirrored version, which is the case for the counterpulsator. It flattens out the blood pressure curve. It may increase the mean pressure in the arterial system, and it may enhance the take out of more energy from the heart (more than before connecting the device), but it will decrease the maximum systolic pressure. Thus, the device cannot solve the pressure demand from peripheral organs like the brain and the kidneys, which have an absolute pressure demand in order to survive.
The Purpose Of The Invention And The Solution Of The Problem
The purpose of the present invention is to achieve a device which, as mentioned in the introduction, without adding externalxe2x80x94from outside the bodyxe2x80x94energy, can utilize energy created within the body, for different purposes and in different ways, depending on which disease is actual. Some examples of possibilities to be opened are given:
to correct a diseased heart, by correcting the pump modus of the heart in the way that the PE is decreased;
to make possible, in patients with edema, like for example in patients with ascites, a system to eliminate the edema without control mechanisms;
to control and manipulate natural and artificial openings of the body;
to supply implanted apparatus like pacemakers, electric pulsgenerators like ICD apparatus with power;
to supply computers or similar equipment with energy in order to control implanted electronic equipment which may be in contact with the central nervous system etc.
The purpose is among other to bring back the modus operandi of the heart to a normal pump modus and thereby reduce the lost energy, while the energy delivered to the surrounding (at rest) is constant. These purposes have been solved by the characteristics mentioned in the patent claims.